We will continue our work on the factors regulating enzyme synthesis and breakdown in animal cells along the following lines: 1) By following changes in the activity of free and complex-bound aminoacyl-tRNA synthetase activity in cultured cells derived of cognate amino acids. 2) By determining changes in the level of charging of total tRNAAsn and individual isoaccepting species under conditions (Asparagine deprivation and temperature shifts of mutants with altered asparaginyl-tRNA synthetase activities) which lead to derepression of asparagine synthetase activity in CHO cells. 3) By measuring rates of synthesis and degradation of histidase in inbred mouse strains with apparently abnormal regulation of histidase levels. We will also attempt to map the relevant genes and to determine the effects of changes in enzyme structure on these parameters.